Golgi stacks are often positioned next to transitional ER sites. However, no mechanistic information is available about how the Golgi is positioned, or how the ER is divided into distinct subdomains. The budding yeast Pichia pastoris provides an ideal model system for a Fombined genetic and morphological analysis of these questions. This project win employ immunoelectron microscopy to localize marker proteins of the transitional ER and Golgi. Our goal is to preserve both cellular organization and protein antigenicity. To achieve this goal, we hope to perform high-pressure freezing and freeze substitution experiments using the MM facilities.